Such heat exchanger arrangements are used to transfer thermal energy generated in a combustion chamber by the combustion of a fuel/air mixture to a fluid used as a heat transfer medium. To monitor the operation of the vehicle heater, a flame sensor is, in general, provided, which may be arranged in the area of a waste gas discharge opening on the heat exchanger arrangement. Such a flame sensor may be designed, for example, as a photodiode or as a conductivity sensor and is set up to record a flame-out. If a flame-out is recorded, reignition of the fuel/air mixture present in the combustion chamber is, in general, initiated.
When the vehicle heater is started in a cold state, it may happen that substances being transported in the waste gases in the form of vapor, such as, e.g., water, are condensed in the heat exchanger arrangement and collect in the vicinity of the flame sensor, as a result of which the risk arises that the condensation water collected will be whirled up by waste gases flowing past later and will come into contact with the flame sensor. This contact may affect the operating characteristics of the flame sensor in such a way that it sends a flame-out signal to a control device, whereupon the latter initiates, as was explained above, a restart of the vehicle heater, which leads to an at least short-term interruption of the heating operation.